Current processes for the extraction of essential oils and volatile aroma components from plant and other biomass materials are typically batch processes that require a solvent, which is usually either a hydrocarbon-based solvent (e.g. an alcohol or butane) or a high-pressure (e.g. supercritical CO2) gas. Systems employing these processes generally require specialized equipment and a carefully controlled process environment, as the hydrocarbon-based solvents are often highly flammable and any usage of high-pressure gases as solvents presents significant safety concerns. Products extracted from these solvent-based processes and systems frequently contain unwanted constituents and/or ballasts that harm the purity, odor, biocompatibility, and other characteristics of the extracted compounds. As a result, the products generally require additional processing, especially purification and solvent clean-up/recovery, downstream of the extraction process.
The following references generally relate to chemical extraction processes and are incorporated herein by reference in their entireties:    British Patent 635,121, entitled “Improvements in or relating to the preparation of extracts from aromatic plants,” issued 5 Apr. 1950 to Germinal S.A.    U.S. Pat. No. 7,622,140, entitled “Processes and apparatus for extraction of active substances and enriched extracts from natural products,” issued 24 Nov. 2009 to Whittle et al. (“Whittle”).    S. Casano et al., “Variations in terpene profiles of different strains of Cannabis sativa L.,” 925 Acta Horticulturae 115 (December 2011).    S. Elzinga et al., “Cannabinoids and terpenes as chemotaxonomic markers in Cannabis,” 3 Natural Products Chemistry & Research 181 (July 2015) (“Elzinga”).
Previous methods and systems, including but not limited to those disclosed in Whittle, have attempted to overcome the above-identified limitations. However, these attempts have their own drawbacks; the methods of Whittle, for example, are suitable for extraction of target compounds only at atmospheric or elevated pressures. The 1950 British patent issued to Germinal S.A. details a process, operable only as a batch process, to extract only volatile compounds by condensing them using intense heat and then intense cold, with intended uses for coffee and tea plant extracts.
There is therefore a need in the art for methods and systems for extracting chemical compounds from plant and other biomass materials continuously that eliminate any requirement for hydrocarbon or gaseous solvents or extreme operating temperatures that may damage temperature-sensitive constituents. It is advantageous for such methods and systems to be simpler and safer than present solvent-based methods and systems while simultaneously producing high-purity extracts without requiring further downstream processing. It is further advantageous for such methods and systems to be operable in either a continuous mode or a batch mode, at sub-atmospheric pressures that allow a reduced operating temperature to protect heat-sensitive constituents.